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Health, 2021, 13, 1020-1044
https://www.scirp.org/journal/health
ISSN Online: 1949-5005
ISSN Print: 1949-4998
The Perspective of Acquired Immunity to
Combat against Infectious Diseases: An
Overview
Md. Shahidul Islam1, Irfan Chaudhuri2, Mahadee Al Mobin1, Mobashara Islam3,
Md. Shahriar Mahmud4, Md. KutubUddin1, K. M. Ariful Kabir5, Md. Kamrujjaman1,6*
1
Department of Mathematics, University of Dhaka, Dhaka, Bangladesh
2
Department of Chemistry, Colby College, Maine, USA
3
Department of Genetic Engineering and Biotechnology, University of Dhaka, Dhaka, Bangladesh
4
Department of Computer Science & Engineering, State University of Bangladesh, Dhaka, Bangladesh
5
Department of Mathematics, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh
6
Department of Mathematics and Statistics, University of Calgary, Calgary, Canada
How to cite this paper: Islam, Md.S., Abstract
Chaudhuri, I., Al Mobin, M., Islam, M.,
Mahmud, Md.S., KutubUddin, Md., Kabir, There is a long ritual of acquired immunity using physical exercise, a ba-
K.M.A. and Kamrujjaman, Md. (2021) The lanced diet, and pharmaceutical medication to generate immunity against a
Perspective of Acquired Immunity to Com-
particular disease insight into the human body. This paper has extensively re-
bat against Infectious Diseases: An Over-
view. Health, 13, 1020-1044.
viewed the impact of exercise, daily life practice, food selection, and several
https://doi.org/10.4236/health.2021.139077 other issues to improve the immune system that combat infection. Studying
the effect of exercise in varying degrees on the immunity system of humans is
Received: August 13, 2021
well developed and exhibit in this study. It investigates the prevention of
Accepted: September 15, 2021
Published: September 18, 2021
pandemics due to herd immunity and finds the perfect amount of exercise to
boost immunity to its maximum. Besides the life practice, it is also explored
Copyright © 2021 by author(s) and that vaccination can improve and optimize herd immunity.
Scientific Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
Keywords
License (CC BY 4.0). Natural Immunity, Medicated Immunity, Physical Exercise, Vaccination,
http://creativecommons.org/licenses/by/4.0/
Infectious Diseases
Open Access
1. Introduction
December 2019, the planet had been experienced the COVID-19 pandemic, and
therefore the development of a safe and reliable vaccination was urgent at that
critical time [1]. Until August 13, 2021, the COVID-19 pandemic has caused
nearly 4,347,996 deaths and has been 206,234,061 confirmed cases across the
DOI: 10.4236/health.2021.139077 Sep. 18, 2021 1020 Health
Md. S. Islam et al.
world [2]. Almost half of the records of deaths go unreported, as most countries
only record people admitted in hospitals with confirmed infection [3].
The sole hope is that we have to remain alert and depend upon our immunity
system if we want to survive with a healthy life because there is no other alterna-
tive except vaccination. A British study published in The Lancet medical journal
looked at levels of neutralizing antibodies produced in vaccinated people ex-
posed to the Delta, Alpha, and Beta variants [4]. A scientific, clinical, and epi-
demiological studies show the impact of physical exercise on the immune system
[5], but no significant mathematical studies show the effects of physical activity
[6]. The physical body is usually at war with outside threats like viruses, bacteria,
fungi, toxins, and parasites. Despite this chaotic state, our body remains healthy
most of the time by defeating viruses because of a robust immune system that
can be boosted by physical exercise [7].
According to CDC, more than five million Americans have missed their
second doses of the Pfizer/Moderna COVID-19 vaccines [8] [9]. From almost
8% of those who got the first shot, some people are feared the side effects, such
as flu-like symptoms, while others said that they felt a single shot was enough
protection against the virus. In other cases, vaccine providers were forced to
cancel second-dose appointments because they did not have enough supply [10].
The COVID-19 pandemic creates unprecedented health and social challenges
with severe mental illnesses uniquely high risk for vulnerable populations [11]-[18].
In this work, we discussed that physical activity could reduce the severity of in-
fection, significantly COVID-19 [19]-[26], extend insulin sensitivity, and reduce
insulin levels [27]. High insulin levels are linked to inflammation, heart condi-
tion, diabetes, and cancer [22]. High blood pressure, diabetics, and cancer pa-
tients are vulnerable to COVID [28] [29] [30].
Stress can wreak havoc in our immune system, even eating right, sleeping
enough, not smoking, or drinking, which reduces the body’s ability to beat infec-
tions. An excessive amount of stress can hamper immunity, and when stress lasts
for an extended time, it can put in danger with serious health issues, like depres-
sion or anxiety. Even chronic skin issues [31]-[37], so we have to try some stress
management techniques to tackle it [27] [38].
Yoga can play an essential role in preventing and managing any disease like
coronavirus by enhancing the immune system, which is also very helpful for de-
pression, anxiety, and stress management [39]. When the immunity is robust
regardless of what infection it is, whether bacterial or viral, it will remain healthy
and guarded [40]-[54].
Harvard researcher Sara Lazar found that 40 - 50 years old meditators have
critical brain structures almost like those of non-meditators of 20 years old young
men. It improves focus, problem-solving power and emotional regulation, and
survival instincts [55] [56]. If anyone is doing physical activities, especially yoga,
breathing exercise, or meditation, they will reduce the health risks [57]-[70].
In this work, we discussed the physical activity that can reduce the infection of
COVID-19 [71]. Physical activities extend insulin sensitivity and reduce insulin
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Md. S. Islam et al.
levels, including aerobics, strength training, and endurance exercise [72]. The
combination of aerobic exercise training and resistance exercise (REX) may be
more effective than either exercise mode alone. A significant advantage of exer-
cise is its ability to scale back insulin levels and increase insulin sensitivity [30]
[73] [74] [75]. Insulin may be a hormone that has several functions, allowing
cells to require up sugar and amino acids from the bloodstream, which are then
used for energy and maintaining muscle. High insulin levels are linked to in-
flammation, heart condition, diabetes, and cancer [76] [77]. High blood pres-
sure, diabetics, and cancer patients are vulnerable to COVID. If people are doing
physical activities, yoga or breathing exercises will reduce the risk [19].
We show that stress can wreak havoc in our system, even eating right, sleep-
ing enough, not smoking or drinking, which reduces the body’s ability to beat
infections. Stressing an excessive amount of over something can hamper im-
munity and health [78] [79]. So, if someone discovers constantly stressed, they
want to try some stress management techniques to tackle it. When stress lasts
for an extended time, it can put the patient in danger for a few pretty severe
health issues, like high vital signs, depression or anxiety, and even chronic skin
issues [80].
Physical activity is regarded as one of the most important aspects of a healthy
lifestyle [81]. A possible advantage of physical exercise in lowering communica-
ble diseases, particularly viral pathologies, has been postulated [82], in addition
to functions linked to the control of excess body weight, systemic inflammation,
and chronic non-communicable diseases. Physical activity, both acute and
chronic, significantly impacts the immune system [83] [84]. According to stu-
dies, the immunological response to exercise is modulated by characteristics
such as regularity, intensity, duration, and type of effort applied [82] [85]. Mod-
erate-intensity physical activities enhance cellular immunity, whereas extended
or high-intensity workouts without adequate rest reduce cellular immunity,
making people more susceptible to infectious diseases [83] [84]. The immuno-
logical decline happens after 90 minutes of moderate- to high-intensity physical
activity, according to the International Society for Exercise and Immunology
(ISEI) [86].
Increased immune vigilance and improved immune competence, which aid in
pathogen control, are two benefits of regular and appropriate intensity exercise
for the immune system in respiratory infections [87] [88] [89] like COVID-19.
Other positive effects on host factors, such as reduction in oxidative stress, in-
creased physical and cardiopulmonary conditioning, attenuation of systemic pro-
inflammatory and pro-thrombotic states, the prevention or reduction of over-
weight, improvements in glycemic, insulinemic, and lipidic metabolisms, in ad-
dition to the enhancement of the vaccination response, show how well ph works
[90].
It is rightly said by the Nobel Prize-winning biologist Joshua Lederberg, “The
single biggest threat to man’s continued dominance on the planet is the virus.”
The human body is an incredible piece of architecture with systems that have
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Md. S. Islam et al.
always perplexed researchers due to its unique capacity to adapt to changing
circumstances. It has a defensive system to defend it from pathogens of all kinds,
especially viruses. “The Immune System” is the name given to this system. The
body must first detect the threat, whether it is a pathogenic agent or an immu-
nization, as with any immune system challenge. The innate immune system is
usually responsible for the initial detection, though B-cells may also be involved.
When the immune system detects epitopes on antigens, the detection process
begins. Epitopes on antigens are tiny sub-regions that simulate immune recogni-
tion. The innate immune system will then respond to the stimulus in a variety of
ways. These innate immune components will opsonize or bind to the agent, as-
sisting antigen-presenting cells like macrophages or monocytes engulfing it. These
antigen-presenting cell(s) will next digest the pathogenic agent’s antigens and
insert them, together with the MHC protein, onto the antigen-presenting cell’s
surface [91]. If the antigen is a viral antigen, it will be linked to MHC I protein
and presented to a CD8 cell by the antigen-presenting cell, triggering cell-mediated
immunity. Suppose the antigen is a bacterial or parasite antigen. In that case, it
will be linked to MHC II protein and given to a CD4 cell by the antigen-presenting
cell, triggering an antibody-mediated response [92].
All cells, including those in the immune system, require adequate and proper
nourishment to function optimally. During infection periods, an “activated”
immune system boosts the need for energy even more, with higher basal energy
expenditure during fever, for example. As a result, optimal nutrition for the best
immunological outcomes would be nutrition that supports immune cell func-
tions, allowing them to initiate effective responses against pathogens while also
allowing them to resolve the response quickly when necessary and avoiding any
underlying chronic inflammation. The immune system’s energy and food re-
quirements can be satisfied through exogenous sources, such as the diet, or en-
dogenous ones, such as body storage if dietary sources are insufficient. Some
micronutrients and dietary components have essential roles in developing and
maintaining a healthy immune system throughout life and reducing chronic in-
flammation. The amino acid arginine, for example, is required for macrophages
to produce nitric oxide. At the same time, the micronutrients vitamin A and zinc
govern cell division and hence are required for an excellent immune system pro-
liferative response. Undernutrition, whether due to food shortages or famines in
developing nations, or malnutrition resulting from periods of hospitalization in
rich countries, is widely known to decrease immune function. The degree of the
deficit, if there are nutrient interactions to consider, the presence of illness, and
the person’s age will all influence the severity of the impairment [28]. A single
nutrient, like vitamin E, can have several immunological effects, such as func-
tioning as an antioxidant, inhibiting protein kinase C activity, and potentially
interacting with enzymes and transport proteins [29]. Excessive intake of several
micronutrients has also been linked to weakened immunological responses. In
malaria-endemic areas, for example, iron supplementation can increase morbid-
ity and mortality. In addition to the potential for nutrition to effectively treat
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Md. S. Islam et al.
immune deficiencies caused by inadequate intake, there is much research to see
if specific nutritional interventions can improve immune function in sub-clinical
situations and thus prevent the onset of infections or chronic inflammatory dis-
eases [93] [94]. The following diagram (Figure 1) shows the flow of how can
improve the immune system.
2. Immune System
A sophisticated and complex mechanism in the human body is alert and active
throughout the day to ensure the body’s safety against all sorts of diseases and
pathogens in its surroundings, termed the “immune system” of the body. The
human immune system can be roughly divided into three layers. The first layer
consists of skin, cilia, and mucus in the respiratory tract; acid and enzymes in
the stomach; lactic acid in the vagina; lysozyme enzyme in tears, saliva, urine,
and sweats and blood clotting on skin being exposed to the outside due to lace-
ration or pricking. The main task of this layer is to trap the invading dust par-
ticles, germs, and bacteria from entering the body at all and flushing them out in
the instance they manage to get in through any opening. The second layer con-
sists of lymphocytes and phagocytes; the complement system comprises 25 dif-
ferent defense proteins; interferon and histamine. Whose essential function is to
kill any foreign particle on-site and alert the whole system to watch out for any
such similar particle to do no further damage by similar such antigen. Anything
that can trigger the immunity is termed an antigen.
The immune system is the body’s innate defense system against attackers.
White blood cells, which mainly consist of lymphocytes, make up the immune
system’s cells. T-cells and B-cells are the two main classifications of lymphocytes.
T-cells have receptors on their surfaces that communicate with molecules present
in other body cells. T-cells recognize the matter in the body as a foreign material,
for example, virus or bacterium, by binding to the molecules. T-cells either kill
the invader individually or collaborate with other immune cells to coordinate an
attack after they have been identified. B cells, on the other hand, produce anti-
bodies that are unique to a foreign substance. The attackers are then tracked
down by the antibodies, which adhere to antigens on the alien substance’s sur-
face. An antibody may either neutralize the foreign agent or label it for destruc-
tion by other immune system members by binding to the antigen.
Furthermore, two forms of the immune system are observed within the body:
the innate immune system and the adaptive immune system. The natural im-
mune system is from birth and includes macrophages, dendritic cells, biological
Figure 1. The flow diagram to improve the immune system.
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Md. S. Islam et al.
kill cells, neutrophils, and cytokines. At the same time, the adaptive immune
system can be changed and increase and decrease in levels. The cells that are a
part of the adaptive immune system include T & B lymphocytes and their prod-
ucts (antibodies and cytokines).
In addition to B-lymphocytes and T-lymphocytes, another type of white blood
cell helps fight infection called macrophages. Macrophages are white blood cells
that destroy foreign cells such as germs, viruses, and dead or dying cells. Ma-
crophages then leave behind parts of the invading cells called antigens. The body
can make corresponding antibodies that recognize and foreign antigens and at-
tack them, stimulating an immune response. Creating the corresponding anti-
body against the alien virus such as COVID-19 can take time and typically re-
quires several days. It can take even longer for the body to fight off the foreign
invader from creating the antibodies. After the body has fought off the foreign
invader, a few T-lymphocytes, or memory cells, go into action rapidly if the body
comes in contact with the same virus again. Thus, the body is quickly able to at-
tack the foreign cells before they can accumulate. Thus, providing a form of
immunity from the foreign pathogen [28].
2.1. Impact of Hormones in the Human Immune System
The presence of hormones influences the immune system’s activity. Hormones
secreted by almost all glands play a part in keeping us fit and sustaining stable
and controlled internal physiological habits, both directly and indirectly. Re-
searchers discovered many times that sex hormones from the reproductive sys-
tem (Testes, Ovary, Uterus, Placenta) influence the immune system due to hor-
mone receptors on immune cells [95]. As their experimental data suggests, when
sex hormones (hormones released from Testes, Ovary, Uterus, Placenta as shown
in Table 1) and immune cells make an interaction. These Cytokines’ releases
determine the number of physical factors called proliferation/apoptosis, diffe-
rentiation, and maturation of different types of immunecytes resulting in in-
flammatory or autoimmune diseases. American Cancer Society reported in 2019
that these Cytokines help boost anti-cancer activity by sending signals that can
help make abnormal cells die and normal cells live longer [96]. Therefore, sex
hormones positively affect the immune system in various ways by increasing the
number of circulating immune cells and triggering the hormones required to
strengthen the immunity.
On the other hand, the endocrine system uses the hormones released to coor-
dinate and monitor internal metabolism, energy levels, fertility, and the body’s
reaction to damage, stress, and diseases it is likely to avoid. A network of signal
molecules (cytokines, hormones, and neurotransmitters) that function on a sim-
ilar collection of receptors connects the immune, endocrine, and central nervous
systems. The following figure (Figure 2) shows the influence of different tech-
niques on the immune system. There is a bidirectional influence between the
immune and CNS (central nervous system or brain) and the immune and endo-
crine system and CNS. Researchers found that sex hormones act directly on the
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Md. S. Islam et al.
Table 1. Source glands and organs of hormones.
Role in
Gland and Organ Released Hormones
Immunity
Growth hormone (GH), Thyroid Stimulating
Hormone (TSH), Adrenocorticotropic hormone
Central Nervous System:
(ACTH), Follicles-stimulating hormone (FSH), Yes
Pituitary gland (brain)
MSH, Luteinizing hormone (LH), Prolactin,
Vasopressin, Serotonin, Endorphin
Central Nervous System: TRH, CRH, GHRN, Dopamine,
Hypotha-lamus (brain) Somatostatin, Vaso-pressin, Oxytocin
CNS: Pineal gland (brain) Melatonin Yes
Thyroid and Parathyroid T3, T4, Calcitonin, Parathyroid hormone (PTH)
Gastrin, Ghrelin, Histamine,
Stomach
Somatostatin, Neuropep-tide Y
Thymus Thymopoietin
Pancreas Insulin, Glucagon, Somatostatin
Kidney Calcitriol. Renin, Erythropoietin
Testes Androgens, Estradiol, Inhibin
Uterus Prolactin, Relaxin
Ovaries, Placenta Estrogens, Progesterone
Androgens, Glucocorticoids,
Adrenal Yes
Adrenaline, Noradrenaline
Liver IGF, THPO Yes
CNS or brain or on the brain hormones that affect the immune response [97].
Therefore, the hormones and glands that have a direct impact on the immunity
system are, Central Nervous System (Pituitary and Hypothalamus glands), Re-
productive organs (Testes, Ovary, Uterus, Placenta glands), Adrenal gland, Pan-
creas glands, and Kidney released hormones (Table 1).
According to Dr. Ananya Mandal, published in the News Medical, hormones
are chemical messengers secreted directly into the blood, which carries them to
organs and tissues of the body to exert their functions. There are many types of
hormones that act on different aspects of bodily functions and processes. Some
of these include [98] [99]:
Development and growth: Pituitary gland hormones.
Metabolism of food items: Insulin, the hormone released from the pancreas.
Sexual function and reproductive growth and health: testosterone, estrogen.
Cognitive function and mood: Dopamine, Serotonin, Oxytocin, etc.
Maintenance of body temperature and thirst: Hypothalamus hormones.
Maintaining salt and water balance of the body: Adrenal gland hormones.
Reduce feeling with pain and help to deal with stress: Endorphins.
Affects immunity: Hormones released from Uterus, Ovary or Placenta and
CentralNervous Systems or brain (Pituitary, Hypothalamus, Pineal).
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Md. S. Islam et al.
Figure 2. Immune System from first antigen exposure to the formation of anti-bodies [103].
2.2. Hormones for a Better Mood
Physical exercise improves many health effects, including mental health and a
positive impact on serotonin levels in the brain, improves mood to enhance ap-
petite and sleep patterns better, and increases dopamine levels [100]. Aerobic
exercises, such as walking, running, swimming, bicycling, fast walking, jogging,
and light hiking, seem to be the most important. Meditation is well-known for
its many health effects, including improved sleep and stress reduction (Figure
3). Meditation has the effect of helping to balance hormone output, especially
dopamine, which negatively influences mood and physical health. Dopamine
and serotonin synthesis may be affected by daily stress (Figure 4, Figure 5). It is
rightly said that “Laugh is the best medicine.” It can benefit by reducing anxiety
and stress and improving low mood by increasing dopamine and endorphin le-
vels [101] [102] [103].
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Figure 3. Immune system has different ways of fighting infection [103].
Figure 4. Human body hormones [99] [104].
Figure 5. Hormones from endocrine and CNS (brain) with significant effect in immune
system.
Dopamine: Dopamine is a chemical that carries impulses from the body to
the brain and is known as the “feel-good” hormone. It is an integral compo-
nent of the brain’s reward system. Dopamine is responsible for influencing a
person’s actions and emotional reactions and is linked to pleasurable sensa-
tions such as finishing a task, celebrating, and consuming food. Dopamine
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balance is essential for physical and mental health, and a lack of it can sub-
stantially affect a person’s quality of life, physically and mentally. If they are
worried about their dopamine levels, some drugs and therapies can help alle-
viate symptoms.
Serotonin: Serotonin is a neurotransmitter that regulates mood, thoughts,
sleep, appetite, metabolism, learning capacity, memory, and hormonal func-
tion. It may be increased by meditation, exercise, and sun exposure, among
other things. Researchers conclude that low serotonin levels play a role in
depression.
Oxytocin: Oxytocin, also known as the “love hormone” is a hormone pro-
duced in response to sexual attraction and is essential for reproduction,
breastfeeding, and close parent-child bonding. In relationships, this hormone
can aid loyalty, empathy, and bonding.
Endorphins: Endorphins, the body’s natural pain reliever, increase reward-
producing behaviors and are produced in response to stress or discomfort.
Cortisol: Cortisol is the body’s primary stress hormone, a naturally occur-
ring steroid hormone that regulates anxiety, motivation, and anxiety by in-
teracting with various brain areas. It helps the body manage carbs, fats, and
proteins, reduces inflammation, lowers blood pressure, raises blood sugar,
regulates the sleep/wake cycle, improves stamina so we can withstand stress,
and restores equilibrium. Cortisol receptors absorb and use the hormone in
a variety of ways. For example, cortisol can change or shut down functions
while the body is on high alert. The digestive and reproductive systems, the
immune system, and also development cycles are examples of these. The
amount of cortisol should decrease, and the pulse, blood pressure, and other
body systems should return to normal. It may also cause a variety of health
issues, such as anxiety and depression, headaches, heart failure, memory and
attention problems, digestive issues, difficulty sleeping, weight gain, and so
on. Cortisol levels fluctuate during the day. Cortisol levels in the body
usually are highest in the morning and lowest at night. Cortisol levels can
also fluctuate; they are secreted in higher amounts during the body’s stress
response and are responsible for various stress-related changes. Stress man-
agement can help to lower cortisol levels in the body. To maintain cortisol
levels stable and under control, stimulate the body’s calming response once
the fight or flight response has occurred, calm the body with various stress
relief strategies, and make behavioral adjustments to prevent the body from
responding to stress in the first place. Breathing exercises, exercise, listening
to music, meditation, yoga, and other relaxation techniques may help the
body retain stable cortisol levels. Learning stress control strategies and
maintaining a low-stress lifestyle is particularly critical. While cortisol is an
essential and beneficial part of the body’s stress response, it is also essential
for trigger the calming response so that the body’s functions can return to
normal after a traumatic incident.
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3. Improving Immune System by Physical Activities
The practice of physical exercises acts as a modulator of the immune system in
the body. During and after physical activity, pro and anti-inflammatory cyto-
kines are released, lymphocyte circulation increases, as well as cell recruitment
[104] and thus, improves sensitivity to Leptin and Insulin, which strengthens the
immune system of the body [77] [78]. Research [105] found that the impact of
exercise on innate and acquired immune parameters consisting of magnitude,
the direction of changes, and recovery time is dependent on the intensity of ex-
ercise that a person consumes or undergoes [106]. For example, when an athlete
participates in high-performance sports, the duration and load of training are
much intense.
Immune function can be compromised at the high-performance end of the
physical activity spectrum and place an individual at increased risk of infection,
as demonstrated in Figure 3. However, there is a general concept that regular
bouts of up to 45 minutes of moderate exercise benefit the host immune defense
(Figure 6). The study was carried out on animals and human beings, particularly
in older adults and people with chronic diseases. Consequently, several clinical
and epidemiologic data based on scientific research supports the impacts of ex-
ercise on the immune system, including the American College of Sports Medi-
cine position papers and the Surgeon General’s report on physical activity and
health [107]. However, these effects are highly variable, depending on the nature
and intensity of exercise. The authors currently define vigorous exercise as 5 to
60 minutes at 70% to 80% aerobic capacity and moderate exercise as 5 to 60 mi-
nutes at 40% to 60% aerobic capacity, which plays a positive role in building the
body’s immune systems [28].
The benefits of moderate exercise (20 to 30 minutes), 55% - 70% of max pulse
rate—have improved the adaptive immune system. Moderate exercise promotes
the flow of lymph and the immune cells and antibodies. Lymph vessels depend
on body motion to move the lymph along. It improves the blood flow of the car-
diovascular system, helping to flush toxins and germs from the body through the
excretory system via urine and sweat. It increases the delivery of oxygen through
the bloodstream, improving the body’s resistance. Exercise also decreases the in-
flammation in the body, which in turn improves immunity. Studies done on
Figure 6. Model of exercise workload/stress continuum, showing the relation between
immune surveillance measures and risk of illness as the exercise workload is increased
from moderate to heavy and overload.
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mice have shown that mice who exercised regularly had less severe symptoms
than those who did not regularly exercise [108]. Lastly, exercising can relieve
mental and emotional stress linked to suppressed immunity and increased ill-
ness.
Yoga is a mind-body tradition that originated in ancient India about 500 BC
to form effective relaxation and spiritual activities. Yoga is a Sanskrit term that
means “unity” or “conjunction” and refers to the concept of uniting the body,
mind, and spirit. It is gaining popularity as a therapeutic intervention, and it
evolved not only as a method of physical exercise but also as a system of healing
[39]. Yoga practice can be beneficial because it blends the benefits of physical
exercise with the help of mindfulness. Studies show that Yoga can improve
cell-mediated immunity. As a result, it may potentially treat diseases like AIDS
or improve immune function in general, such as counteracting immune function
suppression in challenging conditions [36].
About three decades of research has shown the effectiveness of yoga activities,
including mediation, in restoring homeostasis in non-communicable diseases by
reducing stress and encouraging a safe lifestyle. The interconnectedness of the
mind and body and the correction of imbalances have been extensively re-
searched to establish a systemic basis for human well-being. Asana, pranayama,
and meditation are yoga exercises that can help cultivate the mind by streng-
thening the willpower that makes the immune system healthy. Both yoga activi-
ties include intense relaxation, which can help relieve pressures and strains,
which can help avoid immune suppression, impairing the body’s resistance to
infectious bacteria and viruses [109].
A new study looks at the connection between exercise and mental health [41]
[110]. According to research, physical activity can help improve mental health,
and those with serious mental illnesses are less physically active than those in
good mental health. The study discovered that the fear and tension associated
with the COVID-19 pandemic has made people less likely to partake in physical
exercise that may help them improve their emotional health and manage stress,
anxiety, and depression [111]. Stress relief, pain relief, and better sleep have all
become more critical motivators for exercisers. People who had cut their physi-
cal exercise the most after the pandemic had the most mental health problems.
Additionally, more support is needed for those trying to preserve their mental
and physical well-being during difficult periods, such as the COVID-19 pan-
demic, therapeutic support to their physical exercise during hard times to reduce
the pandemic’s pressure avert the mental health crisis [76].
Physical activity and exercise are almost as successful as pharmacological treat-
ments in combating cardiovascular disease and lowering mortality. People with a
severe mental disorder, on the other hand, face a variety of obstacles to physical
activity and fitness, including elevated levels of perceived discomfort, somatic
comorbidities, depressed mood, and a loss of self-confidence and social support,
to name a few [79].
Thus, meditation, exercise, journaling, yoga, adequate sleep, and other mind-
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fulness techniques are some of the activities that can help us control stress [65]
[70] [112]. Whether virtually or in person, seeing a certified psychiatrist or the-
rapist can also be beneficial [80]. Some studies indicate the following supple-
ments may strengthen the body’s immune response [113] [114]:
Vitamin C: According to a review in over 11,000 people, taking 1000 - 2000
mg of vitamin C per day reduced the duration of colds by 8% in adults and
14% in children.
Vitamin D: Vitamin D deficiency may increase the chances of getting sick, so
supplementing may counteract this effect. Adequate levels of vitamin D do
not seem to provide extra benefits.
Zinc: In a review of 575 people with the common cold, supplementing with
more than 75 mg of zinc per day reduced the duration of the cold by 33%.
4. Artificial Immunity (Vaccination)
Patients who have been physically inactive for at least two years have a higher
risk of death from covid. A study said covid patients who were physically inac-
tive or did not exercise were more likely to be taken to hospital, intensive care
unit or die. The study was published in the British Journal of Sports Medicine.
The study was conducted on about 50,000 people. It has been said that physical
inactivity is one of the health risks of patients with Covid. The average age of the
patients in the study was 48 years. Three out of every five were women. Con-
cerned researchers say that smoking, obesity, and anxiety are also among the
health risks of Covid. “Physical inactivity is a severe health risk,” the study said
[87].
For example, COVID-19 vaccines allow us to develop immunity to the COVID-
19 virus without contracting the disease [115] [116]. As previously said, various
types of vaccines provide defense in different ways. However, almost all vaccines
cause the body’s T-lymphocytes and B-lymphocytes to build a “memory” of how
to combat the same virus if it ever contaminates the body again (Figure 7, Fig-
ure 8).
Figure 7. Diagram of process to achieve herd immunity [47] [104].
DOI: 10.4236/health.2021.139077 1032 HealthMd. S. Islam et al.
Figure 8. Diagram of process to achieve herd immunity.
After initial injection, the body usually needs a few weeks to develop and
produce T-lymphocytes and B-lymphocytes. Since the vaccine takes some time
to take its full effect, a person can become infected with the COVID-19 virus
shortly after vaccination. Other symptoms, such as fever, muscle aches, etc., may
appear after immunization, but this is just a common indication that the body is
developing immunity to the virus.
The vaccines operate in various ways to get our bodies to know and defend us
from the COVID-19 virus. No COVID-19 vaccines can give us COVID-19.
There are three main types of COVID-19 vaccines that are existent which are as
follows:
mRNA vaccines: Genetic materials of the COVID-19 virus are put into the
body that gives our cells the tools necessary to make proteins unique to the
virus. Upon completing the instructions to synthesize the proteins that are
unique to the virus, our body then destroys the genetic material from the
vaccine. Our body can recognize the foreign protein and build up the cor-
responding T-lymphocytes and B-lymphocytes to fight the virus if ever found
in the body.
Protein sub-unit vaccines: A sub-unit vaccine introduces one or more anti-
gens to the immune system without adding entire or fragmented pathogen
particles. Antigens may be any compound, such as proteins, peptides, or
polysaccharides, and the term “sub-unit” merely means that the antigen is a
fragment of the pathogen. The vaccine is absolutely “dead” much as inacti-
vated vaccines and therefore poses a lower risk. Instead of injecting the
whole germ, a sterile spike protein present in the virus’s wall is used as a
protein subunit vaccine. Our immune system acknowledges that the pro-
teins are foreign to the body and begin to produce T-lymphocytes and anti-
bodies in response to vaccination. Even if we are contaminated in the future,
our memory cells will recognize the infection and will be able to fend it off
quickly.
Vector vaccines: The vaccine is a weakened variant of a live virus that is not
the COVID-19 virus but contains genetic material from the COVID-19 virus.
If the viral vector has entered the body, the genetic material instructs cells to
produce COVID-19-specific proteins. Our body’s cells can create copies of the
DOI: 10.4236/health.2021.139077 1033 HealthMd. S. Islam et al.
protein using these instructions enables our T-lymphocytes and B-lymphocytes
to know how to battle the virus in the future if they become infected [117].
5. Natural Immunity and Hard Immunity
Herd immunity is described as when a large percentage of a population becomes
resistant to an infectious disease, decreasing the disease’s ability to spread. It is a
resilience made up of blood proteins that our bodies resist foreign invaders, in-
cluding bacteria and viruses. Antibodies combat these invaders by increasing
body temperature, killing bacteria or viruses, and protecting us from illness. To
gain herd immunity, 70% - 90% of a population must have immunity, depending
on how infectious the virus is. Suppose we assume that 80% of a population is
immune to infection. In that case, this implies that 4 out of every five individuals
who come into contact with an infected individual will not become infected (and
therefore will not transmit the disease). In this way, infectious disease transmis-
sion is slowed or eradicated in some particular cases.
Herd immunity (naturally or artificially) is achieved chemically, while the
human immune system is the body’s protective system against foreign patho-
gens, which is a standard and by-born phenomenon (Figure 3). However, sever-
al evidence-based preventive strategies to strengthen the immune system include
eating healthy, exercise and physical activities, and managing stress. Recently, J.
J. Rucklidge, a professor at the University of Canterbury, and G. Schofield, pro-
fessor at the Auckland University of Technology, identified three modifiable risk
factors [71] as shown in Table 2.
Table 2. Ways to get a stronger immune system before we perceive a herd immunity.
Diet Exercise Relieve from Stress
Meditation, mindfulness,
Vitamins C and D, as well as High cardio-respiratory
cognitive-behavioral therapy,
zinc, have been described as (lung and heart) health is
getting enough sleep, and eating
important for improving linked to less respiratory
a healthy diet will all help us cope
immunity during one’s life. ailments and longer survival.
with the negative effects of stress.
Consuming real entire foods Receiving adequate nutrients like B
such as fruits and vegetables, Budget time and priorities vitamins and a broad spectrum of
almonds, legumes, fish, and walking at a minerals like magnesium, copper,
healthier fats while avoiding Minimum. and zinc at periods of stress has a
ultra-processed foods. beneficial effect onphysical health.
In both children and adults, Engage in and perform a
Immunity is negatively affected
a nutritious and more vigorous activity
by stress. It causes the cortisol
nutrient-dense diet is linked regularly, in optimum
response to be disrupted, which
to a reduced risk of mental amount. May go outside and
may suppress immune function.
health conditions. be with important others.
Chronic stress may reduce the
Low levels of specific The more the better, as long
number of lymphocytes in the
nutrients, such as vitamin D, as it is not achieved to the
body. An individual is more
have been identified as point of exhaustion for the
likely to catch a virus owing to
COVID-19 risk factors. individual’s fitness level.
poor lymphocyte count.
DOI: 10.4236/health.2021.139077 1034 HealthMd. S. Islam et al.
The natural yet risky way to attain immunity is by being infected by the dis-
ease. Resilience against infectious viruses is developed generally due to surviving
viral infections; this provides the requisite antibodies to fend off potential infec-
tions. A vaccination will give a person artificial immunity to a disease, prevent-
ing the virus from spreading to those that cannot be vaccinated, such as new-
borns, pregnant mothers, and people with pre-existing medical conditions. On
the other hand, herd immunity can be obtained when a sufficient number of in-
dividuals catch the illness and survive. Natural immunity may contribute to
building herd immunity, but it may not be as effective as vaccines, given the
health hazards it can pose to many people [118]. When more people in a com-
munity are immune, a disease cannot move as quickly and is less likely to find
people who lack immunity. Regarding COVID-19, 50% - 80% of people are ex-
pected to remain protected against the virus achieving herd immunity if they
consume the vaccines, a recent article reported [119]. Most people infected with
COVID-19 produce an immune response within a few weeks, but we do not
know how robust or extensive the immune response is, how long it lasts, or how
it varies between people. There have also been cases of individuals infected with
COVID-19 a second, third, or fourth time.
Herd immunity is obtained in two ways: spontaneously or chemically. It oc-
curs when a herd has gained immunity either by vaccination or prior infection.
Recently, the World health organization (WHO) advocates that herd immunity
is achieved by vaccination rather than encouraging an epidemic to spread to any
part of the population. Vaccines work by simulating pathogens in our bodies
and training our immune systems to produce disease-fighting proteins known as
antibodies. Herd protection to COVID-19 is designed to keep nearly 10% of
susceptible populations (pregnant mothers, the very ill, and the elderly) healthy
and shielded from the disease. If we vaccinate 100% of the “target” population,
we will only achieve 50% protection for the whole community; we will not earn
more than 50% - 60% vaccination. If 50% herd immunity is needed, it is clear
that vaccination alone would not be enough to meet the target.
The percentage of the population who must be vaccinated against COVID-19
to achieve herd immunity is unknown. However, it varies depending on the
community, the vaccine, the communities targeted for vaccination, and other
variables. WHO is also factoring in the intensity and duration of a person’s reac-
tion, which varies depending on whether the infection is asymptomatic, mod-
erate, or extreme. In this field, further research is needed. Immune responses can
occur in even asymptotic individuals. Herd immunity is not ensured, even
though 70% of the population is contaminated for herd immunity, which is con-
siderable. To put it another way, more than 120 million individuals would have
to be infected with COVID-19 before herd immunity is achieved. If a 1% death
rate is used, the number of individuals who die will be enormous.
CDC found that the mRNA vaccines developed by Pfizer-BioNTech and
Moderna are highly effective against COVID-19 because, after the first dose,
those vaccines prevented 80 percent cases and 90 percent after the second dose.
DOI: 10.4236/health.2021.139077 1035 HealthMd. S. Islam et al.
Those researchers found that the mRNA vaccine provides immunity for at least
six months, but they cannot be sure if immunity will wane after that or any
booster dose will be needed to take regularly [120].
Vaccines are very effective at preventing severe COVID-19, including asymp-
totic ones. President of American Medical Association Dr. Susan Bailey said,
“There is more evidence showing that transmission of the virus from a vaccina-
tion is likely deficient’’. The good news is that studies showed that vaccines re-
duce transmission to some extent, but they do not know how much the vaccines
will reduce transmission [121]. Pfizer has recently released their data showing
that the vaccine was highly influential in South Africa, where the B.1.351 variant
is common. The New England Journal of Medicine on March 16, 2021, shows
that the Oxford-AstraZeneca vaccine is only 10 percent effective against the
South African variant [122] [123] [124].
Once the people are vaccinated, transmission becomes less and protects
people by reducing disease spread. In Bangladesh till April 8, 2021, 5,498,172
first shot has received, which is about 1.7 percent of the country’s population of
170 million, and we need to give 125,000,000 of 80% of the population. We need
reliable data to understand trends and patterns of death, and the vaccine alone
will not be enough to control the pandemic. The vaccine does not offer imme-
diate protection against disease. The accurate and sufficient data is more impor-
tant in fighting and prevent the pandemic. AstraZeneca said that the second shot
of the vaccine could ensure that more consistent protection reaches 82 percent
efficiency from 76 percent after the first shot. For now, washing hands, wearing
masks, social distancing, physical activities, and other interventions that can re-
duce the rate of the infectious disease remain the best ways to lessen the destruc-
tion of Covid-19 to develop treatments and vaccines, also reduce deaths.
6. Concluding Remarks
We have discussed the physical activity is one of the only effective ways to stop
chronic diseases. The evidence shows that regular physical activity strengthens
the human system, reduces the danger of falling ill and dying from communica-
ble diseases, and significantly increases the effectiveness of vaccination cam-
paigns. Regular physical activity increases the amount of CD4+ T cells, which
are liable for alerting the system of an attack and regulate its response. Physically
active people are less likely to develop obesity, diabetes, respiratory and cardi-
ovascular diseases also reduce stress and chronic inflammation, successively re-
ducing the likelihood of adverse and fatal infections. An ideal diet is also a must
to lead a healthy life. Proper diet boosts immune system, reduces the risk of
mental health condition, gives energy to do physical exercise, and many more.
We also discussed, yoga can play an essential role within the prevention and
management of coronavirus.
Acknowledgements
The authors acknowledged to the anonymous reviewers for their constructive
DOI: 10.4236/health.2021.139077 1036 HealthMd. S. Islam et al.
suggestions to improve the quality of the manuscript significantly. The authors
M. Kamrujjaman and M. Shahidul Islam research were partially supported by
Centennial Research Grant, University of Dhaka.
Author Contributions
Conceptualization, M. S. I, M. K. and K. M. A. K.; methodology, I. C., M. A. M.,
and M. I.; investigation, M. S. I; resources, M. S. M, M. K. U; original draft prep-
aration, I. C., M. A. M., and M. I.; review and editing, M. S. I, M. K. and K. M. A.
K. and M. S. M., supervision, M. K. All authors have read and agreed to the pub-
lished version of the manuscript.
Conflicts of Interest
The authors declare that they have no conflict of interest.
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